The present invention relates to a flexible shaft coupling of the sleeve type.
Transferring power or rotational motion through flexible, elastomeric, sleeve-type, shaft couplings is known. Representative of the art are U.S. Pat. Nos. 2,952,143 and 6,671,475. These couplings allow misaligned shafts to effectively connect and transfer power and absorb some vibration. These couplings generally comprise a pair of opposing hubs adapted to attach to two coaxial shafts, and a connecting sleeve extending between and engaging the two hubs. The hubs and sleeves engage via a plurality of axially extending ribs or teeth along at least a portion of the inner periphery of the sleeve for meshing with grooves in oppositely disposed hubs or end pieces to form a flexible coupling assembly. These couplings generally provide some vibration isolation and accommodate some shaft misalignment.
Problems with these flexible sleeve couplings include that elastomer teeth can shear off under a torsional load, the sleeve itself can shear into two pieces in the area intermediate between the two engaged ends, and the sleeve can expand or explode at high speed from centrifugal force. Another problem is the failure to transfer power or motion after one of the aforementioned problems occurs. Known methods to improve tooth shear resistance include to reinforce the elastomer of the sleeve with chopped or continuous fibers, to use higher strength plastics, composites or elastomers, or to reinforce the teeth with fabric. Representative of the art is U.S. Pat. No. 6,283,868. Another approach to strengthen the teeth is to provide rigid projections on the two hubs which overlap or intermesh, with the elastomer engaged between them in compression whenever torque is applied to the coupling, thus changing the mode of coupling altogether as disclosed in U.S. Pat. No. 3,362,191. Known methods to protect the sleeve from centrifugal forces include to reinforce the sleeve with tensile cords as disclosed in U.S. Pat. No. 6,283,868, to provide the hubs with an annular cavity into which the sleeve engages as disclosed in U.S. Pat. No. 5,660,591, and to provide an external metal band as disclosed in U.S. Pat. No. 3,362,191. Known methods to prevent the sleeve from shearing between the hubs include using one inner male hub and one outer female hub with the annular sleeve engaged there between as disclosed in U.S. Pat. No. 4,357,137, and thickening the intermediate region of the sleeve as disclosed in U.S. Pat. No. 6,671,475. A known method to provide fail-safe transmission of power on failure of the elastomer is to provide a rigid engaging element which may be metal coated with elastomer as disclosed in U.S. Pat. No. 5,660,591. Because the elastomer layer is so thin, this fail-safe coupling provides very little flexibility and very little vibration isolation. The use of textile reinforcements complicates the manufacturing of the sleeve, and external metal bands increase the number of discreet parts in the assembly. Annular cavities increase the bulk or complexity of the hubs.
What is needed is an improved sleeve coupling which has improved tooth shear resistance, preferably in a one piece sleeve without complicated manufacturing steps or a plurality of parts. What is needed is an improved elastomeric coupling sleeve which combines vibration isolation and accommodation of shaft misalignment, with high-speed resistance, and increased torque resistance. What is needed is a polymeric, toothed sleeve, integrally reinforced with a rigid material such as a metal band having a plurality of tooth-reinforcing fins or protrusions. What is needed is a shaft coupling assembly wherein a vibration-damping and/or misalignment-absorbing elastomeric sleeve has a rigid reinforcing member that increases the shear resistance of the sleeve by placing the elastomer in some degree of compression during use.
The present invention meets one or more of these needs by providing a metal support along with a polymeric coupling sleeve. The metal support, in the shape of a round band (like a section of tubing) has protruding fins. There is a fin in a coupling tooth. As a result of this metal support, when the coupling is engaged, the tooth polymer undergoes compressive stress, which is the best type of stress for elastomers (in contrast to shear, tensile, and bending stresses). The polymeric material is compressed against the metal fin, rather than undergoing shear stress as in prior art sleeve couplings. The compressive resistance of the polymer improves the isolating properties of the coupling. The polymer can be tuned to obtain the desired stiffness and isolating properties.